Journal of the Rubber Research Institute of Sri Lanka (2019) 99, 126-141
126
Assessment and selection based on girth and yield performance
of new Hevea genotypes generated from controlled hybridization
P V A Anushka*, S P Withanage**, N P S N Karunaratne**,
K V V S Kudaligama**, T T D Dahanayake** and H P Peiris**
* 25/A, Capron Street, Crawley, WA 6009, Australia
** Rubber Research Institute of Sri Lanka, Dartonfield, Agalawatta, Sri Lanka
Abstract
The objective of this study was to evaluate the girth and yield performance of new
Hevea genotypes obtained from the 1998 hand pollination (HP) program. Sixty-five
new genotypes were assessed along with the control clones viz. RRIC 121, RRIC 130
and RRISL 205. Dry rubber yield for six years, annual girth at the 14th year and girth
increment, percentage of tappable trees, survival trees and tapping panel dryness
affected trees and latex properties of selected genotypes were evaluated. Considering
the results, 63% of the genotypes were recorded as significantly higher or similar
average yield compared to control clones. The genotypes, 98-80 and 98-219 were the
top-rankers with average yields of 53.7 g and 52.0 g per tree per tapping, respectively.
Moreover, the progeny generated from 1998 hand pollination consisted of good
yielders similar to the yield of the clone RRIC 121 and could be considered as potential
candidates for future clonal selection programmes to develop elite clones. Eighty-two
percent of the genotypes showed significantly higher or similar mean girth compared
to controls. Genotypes, 98-276 and 98-68 were ranked at number one and two, which
have obtained respective girth values of 80.6 cm and 76.5 cm. Eighteen percent of
genotypes recorded more than 70 cm of mean girth, which was an indicator of the
development of vigorous timber clones in the future. Moreover, these genotypes
possess high yield potential. Almost all the genotypes had significantly high girth
increment during the immature phase than the post tapping phase. Genotypes 98-80
and 98-219 had performed well based on the dry rubber content (DRC), sucrose and
inorganic phosphorus values. In conclusion, the 1998 HP programmes has generated
a valuable pool of genotypes that have paved the path to producing outstanding Hevea
clones.
Key words: controlled hybridization, genotypes, girth, Hevea brasiliensis, tapping panel
dryness, yield
Introduction
Almost all the popular clones available
in major rubber growing countries are
entirely developed through conventional
breeding procedures (Reju et al., 2016)
and the hybridization is a major
conventional breeding procedure in
rubber breeding other than introduction
DOI: http://doi.org/10.4038/jrrisl.v99i0.1895
P V A Anushka et al.
127
and selection (Goncalves et al., 2007 &
2011). The breeding procedure is mainly
focused on developing high yielding
clones. Yet, other characteristics such as
vigour and disease resistance are also
considered. Breeding trials related to
natural rubber research in Sri Lanka is
done mainly in three stages. In the first
stage, a progeny obtained from the hand
pollination is planted in the nursery and
subjected to preliminary evaluation. The
best genotypes selected from the
preliminary evaluation are then
established in small-scale clonal trials
(SSCTs) as the second stage. For SSCTs
bud grafted genotypes are used with 15-
20 replicates from each genotype along
with recommended clones as controls. It
takes approximately 10-12 years to
select the best performing genotypes
from SSCTs and the selected genotypes
are incorporated to Estate/RRI
colaborative trials (ECTs) at the third
stage. It takes another 10-12 years to
select outstanding genotypes from the
ECTs and to include in the Group III of
RRISL clone recommendation. It will
take another 20-25 years to upgrade new
clones into Group II and Group I
respectively, from Group III. However,
this procedure takes many more years to
reach a clone up to Group I. Thus,
currently only five clones represent
group I and these clones occupy a large
share in the rubber sector in Sri Lanka.
Department of Genetics and Plant
Breeding of RRISL involve in the annual
hand pollination procedure to improve
genotypes through hybridization to
increase the number of clones along with
the interim clone recommendation
procedure to solve this problem. Under
interim clone recommendation, Group II
and III clones are also evaluated in
smallholder level in addition to estate
level, before up graded into Group I
(Attanayake, 2001 and Withanage et al.,
2014).
During the breeding procedure, both
girth and yield parameters are widely
used as attributes of growth and good
harvesters. Girth is the key factor taken
into consideration for evaluating growth
and attainment of crop maturity for
harvesting (Chandrasekhar et al., 2005).
Average yield is an important factor for
Hevea clonal selection (Reju et al.,
2016). Therefore, at the final stage of
selection, average yield per tree per
tapping is considered as the main
selection criterion.
This article focuses on assessing
genotypes obtained from 1998 hand
pollination programme based on average
girth, girth increment, average yield and
latex physiological properties evaluated
in small-scale clone trials in selecting
best performing genotypes for
developing new clones for future.
Materials and Methods
Location The experiment was carried out at the
Department of Genetics and Plant
Breeding at Kuruwita sub-station,
Rubber Research Institute, Sri Lanka.
Kuruwita is located in Ratnapura district
experiencing a tropical climate which is
favorable for rubber cultivation.
Small-scale clone trial of 98HP
progeny
Two hundred and eighty four seedlings
were generated from 1998 hand
Selection based on girth and yield performance of Hevea
128
pollination (HP) programme by using
clones PB 260 and RRIC 130 as parents.
Better performing seedlings were
selected after evaluating their juvenile
yield (micro tapping), girth, bark
thickness and other secondary attributes
such as disease resistance at the three
years old mother plant nursery. From
these, 65 genotypes were selected and
cloned through bud grafting and the
plants were established in a small-scale
clone trial along with RRIC 121, RRIC
130 and RRISL 205 as controls at the
RRISL sub-station in Kuruwita in 2001.
The small-scale clone trial was
conducted as three separate trials with 22
genotypes and three control clones (25
treatments) per trial. Each trial was laid
according to a completely randomized
design with 16 trees per genotype/clone
(per treatment). Tappability of the
genotypes was determined when more
than 65% of trees under each trial have
reached a girth of 50 cm and beyond. The
trees were opened for tapping at the age
of eight years. The tapping system
followed was ½ SD2.
Measurement of girth, yield and other
growth parameters
Dry rubber yield per tree per tapping in
grams (g/t/t) over six years and girth of
the trees, 14 years after planting were
recorded. Data on average annual yield
in consequent six years were recorded
after opening the panel for tapping by the
cup coagulation method, in two normal
tapping days per month. During the cup
coagulation method 2% acetic acid
solution was added to the latex of
individual trees in the collecting cup and
stirred. Thereafter, coagulated rubber
was pressed and dried until a constant
weight to record the test tapped yield.
Annual girths of the trees were recorded
at the height of 120 cm above the bud
union; which was started during the
second year of planting and were used to
determine the girth increment.
Incidences of diseases were also
assessed by visual observations during
the experimental period. The data on
percentage of survival at the opening of
tapping and the percentage of Tapping
Panel Dryness (TPD) at sixth year of
tapping was calculated. The data on
yield and girth were statistically
analyzed using Analysis of Variance
(ANOVA) followed by mean separation
by Duncan’s Multiple Range Tests using
SAS ver. 9.2.
Measurement of latex physiological
properties
The selected best performing genotypes
and the control clone, RRIC 121 were
subjected to testing of latex
physiological properties. Randomly
selected latex samples (five replicates
from each genotype) were collected to
the vessels, immersed in ice, avoiding
latex dripped for the initial five minutes
after tapping and then serum was
extracted by coagulating 2.5 g of latex in
25 ml of 2.5% trichloro acetic acid
(TCA) and used to quantify sucrose
content (Scott and Melvin, 1953),
inorganic phosphorus content (Taussky
and Shorr, 1953), thiol content (Boyne
and Ellman, 1972) and polyphenol
content (Turkmen et al., 2006). By using
standard ISO method (Anon., 1984), dry
rubber content of latex of each sample
was analyzed.
P V A Anushka et al.
129
Results and Discussion
Yield performances
The values of average dry rubber yield of
all the tested genotypes from three trials
including control clones are given in
Table 1, ranking in descending order. In
the early years of tapping, yield per tree
(g/t/t) is a good indication of the yield
potential than the yield per hectare, due
to wide variations in tappability or
tappable stand per hectare among clones
at opening (Gonçalves et al., 2007).
Mean dry rubber yield varied among
genotypes and controls. Average tree
yield per tapping for six years showed
that yield level among genotypes varied
between 52.0 g and 23.46 g in trial 1,
53.7 g and 23.9 g in trial 2 and 45.1 g
(RRIC 121) and 18.8 g in trial 3.
Genotypes, 98-219 and 98-80 showed
the highest mean dry rubber yields,
which were greater than the control
clone, RRIC 121. There were 33
genotypes above the yield of RRIC 130
and 38 genotypes above the yield of
clone RRISL 205. Collectively, there
were 40 new genotypes (62.5%) which
were superior to the control clones in this
aspect. Genotype, 98-219 of the trial 1
and genotype 98-80 of the trial 2 were
the top-ranking genotypes which have
given the highest mean yield of 52 g/t/t
and 53.7 g/t/t (Table 1).
Table 1. Sixth year average yield (g/t/t) of 1998 HP genotypes along with control clones from
Trial 1, Trial 2 and Trial 3
Trial 1 Trial 2 Trial 3
Clone Average
yield
Rank Clone Average
yield
Rank Clone Average
yield
Rank
98-219 52.04a 1 98-80 53.66a 1 RC121* 45.14a 1
RC121* 51.58ab 2 RC121* 43.66ab 2 98-223 44.90a 2
98-105 48.48abc 3 98-68 43.11abc 3 98-278 39.29ab 3
98-124 47.26abc 4 98-73 41.96abcd 4 98-220 37.11abc 4
98-143 46.46abcd 5 98-58 37.77bcde 5 98-154 35.28bc 5
98-236 45.88abcde 6 98-44 37.26bcde 6 98-200 34.47bcd 6
98-98 44.84abcde 7 98-67 35.83bcde 7 98-30 33.23bcde 7
98-207 40.51abcdef
8 98-74 34.32bcde 8 98-19 33.01bcde 8
98-276 40.29abcdef 9 98-70 33.72bcde 9 RC130* 32.49bcde 9
98-11 40.18abcdef
10 98-51 31.63bcde 10 98-196 32.04bcdef 10
98-89 39.93abcdef
11 98-54 30.88bcde 11 98-222 30.77bcdef 11
98-230 37.83abcdefg
12 RL205* 30.74bcde 12 98-23 30.66bcdef 12
98-237 37.72bcdefg
13 98-62 29.84bcde 13 98-257 29.86bcdef 13
98-135 37.57bcdefg 14 98-37 28.45cde 14 RL205* 29.3bcdef 14
98-84 36.22cdefg 15 RC130* 28.25cde 15 98-18 29.15bcdef 15
RC130* 34.86cdefg 16 98-77 27.20cde 16 98-193 27.53cdefg 16
Selection based on girth and yield performance of Hevea
130
Trial 1 Trial 2 Trial 3
Clone Average
yield
Rank Clone Average
yield
Rank Clone Average
yield
Rank
98-153 32.70defg 17 98-71 26.32de 17 98-15 24.41defg 17
98-164 32.11defg 18 98-41 25.56de 18 98-149 23.57efg 18
98-201 31.92efg 19 98-07 25.48de 19 98-224 23.34efg 19
RL205* 29.13fg 20 98-50 24.53e 20 98-26 22.03fg 20
98-120 29.05fg 21 98-59 24.48e 21 98-12 21.94fg 21
98-83 28.75fg 22 98-55 24.46e 22 98-38 18.88g 22
98-25 24.76g 23 98-64 24.23e 23 98-194 18.79g 23
98-81 24.54g 24 98-56 24.06e 24
98-205 23.44g 25 98-78 23.90e 25
Mean 37.65 Mean 31.98 Mean 30.07
Root
MSE
9.92 Root
MSE
12.48 Root
MSE
8.81
CV 26.36 CV 39.04 CV 29.32
*Control clones: RRIC 121, RRISL 205, RRIC 130
Means followed by the same letter within a column are not significantly different one another
at p < 0.05
There were 13 genotypes along with
RRIC 121 in all 3 trials, that have shown
an average yield higher than 40 g/t/t,
which was nearly 20% from the total
number of genotypes. RRIC 121 is one
of the best performing clones in the
country. In this study, it was always
ranked at the top level among genotypes
in all 3 trials. Thus, 1998 HP progeny
consisted of good yielders comparable
with RRIC 121, which include potential
candidates for the future clonal selection
programmes to release high yielding
clones for the industry.
Girth performances
Average girth at the 14th year and
average girth increment of immature and
post tapping phases were ranked among
the tested genotypes from three trials
including control clones (Table 2 and
Table 3). Average girth at the 14th year
after planting in trial 1, 2 and 3 ranged
from 51.1 - 80.6 cm, 41.3 - 76.5 cm and
55.4 - 71 cm, respectively. Genotypes
98-276 (80.6 cm), 98-68 (76.5 cm) and
98-223 (71 cm) have recorded the
highest girth at the final year of
evaluation, while these genotypes have
represented a mean yield around 40 g/t/t.
P V A Anushka et al.
131
Table 2. Average girth of genotypes and control clones at the 14th year after planting
*Control clones: RRIC 121, RRISL 205 and RRIC 130
Means followed by the same letter within a column are not significantly different one another
at p < 0.05
Trial 1 Trial 2 Trial 3
Clone Average girth
(cm)
Clone Average girth
(cm)
Clone Average girth
(cm)
98-276 80.61a 98-68 76.50a 98-223 71.00a
98-230 72.60ab 98-50 73.11ab 98-200 66.71ab
98-98 72.42ab 98-80 72.93ab 98-26 66.00ab
98-219 71.61bc 98-51 72.19abc 98-18 63.61ab
98-89 70.06bcd RL205* 68.67bcd 98-38 63.35ab
98-84 69.23bcde 98-73 67.25bcde 98-149 63.19ab
RC121* 68.84bcde 98-58 67.03bcde 98-193 62.65ab
98-11 68.47bcdef 98-54 66.50bcdef 98-15 62.17ab
RL205* 68.30bcdef RC121* 66.40bcdef 98-30 62.08ab
98-207 66.86bcdefg 98-71 64.73cdefg 98-278 61.83ab
98-83 66.38bcdefg 98-64 62.37defgh 98-154 61.67ab
98-236 66.10bcdefg 98-44 61.57defghi 98-220 61.04ab
98-143 63.57bcdefgh 98-41 61.23defghi 98-29 61.04ab
98-124 63.06bcdefgh 98-62 60.29efghi 98-194 60.92ab
98-153 62.22cdefghi 98-07 59.11fghij 98-23 60.68ab
98-164 62.03cdefghij 98-77 58.77fghij RL205* 60.60ab
98-105 60.62defghij RC130* 58.29ghij RC130* 60.46ab
98-135 59.73efghijk 98-67 57.81ghij 98-224 59.37ab
RC130* 59.00fghijk 98-56 57.73ghij RC121* 59.05ab
98-25 58.53ghijk 98-70 56.92ghij 98-257 58.87ab
98-201 56.18hijk 98-37 55.10hijk 98-12 58.64ab
98-237 55.00hijk 98-59 53.75ijk 98-19 58.57ab
98-120 53.00ijk 98-74 52.25jk 98-196 56.92b
98-205 52.67jk 98-55 48.17k 98-222 55.44b
98-81 51.08k 98-78 41.28l
Mean 64.06 Mean 61.57 Mean 61.61
Root
MSE
10.90 Root MSE 9.04 Root MSE 13.72
CV 17.02 CV 14.68 CV 22.28
Selection based on girth and yield performance of Hevea
132
Table 3. Average girth increment of genotypes before and after opening for tapping along with the control clones in Trial 1, Trial 2
and Trial 3
Trial 1 – Girth increment Trial 2 – Girth increment Trial 3 – Girth increment
Clo
ne
Bef
ore
tap
pin
g
op
enin
g
Aft
er
tap
pin
g
op
enin
g
Clo
ne
Bef
ore
tap
pin
g
op
enin
g
Aft
er
tap
pin
g
op
enin
g
Clo
ne
Bef
ore
tap
pin
g
op
enin
g
Aft
er
tap
pin
g
op
enin
g
98-276 7.42(1) 1.96 (1) 98-68 7.11 (1) 1.57(4) 98-223 6.25 (2) 2.15(1)
98-230 7 (2) 1.06(15) 98-50 6.53 (6) 2.04 (1) 98-200 6.28 (1) 1.17(11)
98-98 6.93 (3) 1.41 (7) 98-80 7.04 (2) 1.37(7) 98-26 5.89 (6) 1.68 (2)
98-219 6.39 (8) 1.70 (3) 98-51 6.65 (4) 1.65 (3) 98-18 5.97 (4) 0.98(19)
98-89 6.26(10) 1.84 (2) RL205* 6.83 (3) 1.10(10) 98-38 5.74 (11) 1.40 (3)
98-84 6.73 (5) 0.98(17) 98-73 6.15 (8) 1.42 (6) 98-149 5.77 (9) 1.35(4)
RC121* 6.68 (6) 1.46 (6) 98-58 6.58 (5) 0.90(14) 98-193 6.02 (3) 0.9(21)
98-11 6.49 (7) 1.24(9) 98-54 5.67 (16) 1.91(2) 98-15 5.90 (5) 1.03(17)
RL205* 6.92 (4) 0.91(20) RC121* 6.52 (7) 1.09(11) 98-30 5.69 (14) 1.19(9)
98-207 6.33 (9) 1.15(13) 98-71 5.88 (12) 1.53(5) 98-278 5.85 (7) 0.88(22)
98-83 5.78(16) 1.65 (4) 98-64 5.73 (14) 1.22 (8) 98-154 5.72 (13) 1.21(7)
98-236 5.96(12) 1.56 (5) 98-44 6.05 (9) 0.82(17) 98-220 5.68 (15) 1.15(12)
P V A Anushka et al.
133
Trial 1 – Girth increment Trial 2 – Girth increment Trial 3 – Girth increment C
lon
e
Bef
ore
tap
pin
g
op
enin
g
Aft
er
tap
pin
g
op
enin
g
Clo
ne
Bef
ore
tap
pin
g
op
enin
g
Aft
er
tap
pin
g
op
enin
g
Clo
ne
Bef
ore
tap
pin
g
op
enin
g
Aft
er
tap
pin
g
op
enin
g
98-143 6.11 (11) 0.97(18) 98-41 6.04 (10) 0.63(21) 98-29 5.64 (16) 1.08(15)
98-124 5.92(13) 1.17(12) 98-62 5.8 (13) 0.78(20) 98-194 5.73 (12) 0.99(18)
98-153 5.85(15) 1.1(14) 98-07 5.96 (11) 0.47(23) 98-23 5.55 (18) 1.25(6) 98-164 5.92(14) 0.82(22) 98-77 5.7 (15) 0.79(19) RL205* 5.76 (10) 0.88(23)
98-105 5.75(17) 0.95(19) RC130* 5.44 (19) 1.2 (9) RC130* 5.61 (17) 1.05(16)
98-135 5.34(21) 1.29 (8) 98-67 5.64 (17) 0.86(16) 98-224 5.52 (19) 1.18(10)
RC130* 5.57(18) 1.21(11) 98-56 5.43 (20) 1.02(13) RC121* 5.83 (8) 0.71(24)
98-25 5.49(19) 0.88(21) 98-70 5.48 (18) 0.8(18) 98-257 5.51 (20) 1.15(12)
98-201 4.95 (24) 1.23(10) 98-37 5.09 (23) 1.08(12) 98-12 5.46 (21) 1.20 (8)
98-237 5.16 (22) 0.71(23) 98-59 5.1 (22) 0.87(15) 98-19 5.39 (22) 1.11(14)
98-120 5.36 (20) 0.42(25) 98-74 5.12 (21) 0.60(22) 98-196 5.39 (22) 0.90(20)
98-205 4.97(23) 0.68(24) 98-55 4.66 (24) 0.47(24) 98-222 4.93 (24) 1.30(5)
98-81 4.75 (25) 1.04(16) 98-78 3.87 (25) 0.40(25)
*Control clones: RRIC 121, RRISL 205, RRIC 130
Means followed by the same letter within a column are not significantly different from one another at p < 0.05
Selection based on girth and yield performance of Hevea
134
High yielders did not necessarily
associate with high girth increment
(Gonçalves et al., 2011), but according to
the results, some of the high yielding
genotypes such as; 98-219, 98-80, 98-68,
and 98-223 have also recorded higher
girth values. Forty six genotypes (82% of
genotypes) were comparatively superior
to the control clones in terms of girth,
while 18% of genotypes reached above
70 cm, indicating vigorous breeding pool
for timber clones.
Average girth increment of the trees
provides information on the possibility
of the early tappability and vigorous
growth. Girth increment of all genotypes
has represented a high girth increment at
the immature phase compared to post
tapping period. It was clear that tapping
of the bark has slowed down the growth
of the plant. Mean girth increment prior
to opening for tapping ranged from 4.8 in
genotype 98-81 to 7.4 in genotype 98-
276, 3.9 in genotype 98-78 to 7.1 in
genotype 98-68 and 4.9 in genotype 98-
222 to 6.3 in genotype 98-220 in Trial 1,
2 and 3, respectively. Control clone
RRIC 121 has recorded the mean girth
increments of 6.7 (Trial 1), 6.5 (Trial 2)
and 5.8 (Trial 3) before tapping. Around
12% of the genotypes were at the top
ranks achieving an increment of 7
cm/year the girth before opening for
tapping. The mean girth increment
during the tapping period has also varied
among the genotypes and it was
equivalent or less than 2 cm/year for all
genotypes. Genotypes 98-223 (Trial 3),
98-50 (Trial 2) and 98-276 (Trial 1) have
recorded higher girth increments. There
were five genotypes in Trial 1, 10
genotypes in Trial 2 and 23 genotypes in
Trial 3 that have reported higher girth
increments when compared to the
control clone RRIC 121. Gonçalves et al.
(2011) have mentioned that good
girthing rate during tapping is a key
important factor for a sustainable yield
and reduces losses due to wind damage.
Performances of secondary growth
parameters
Recommended minimum girth for
opening of tapping is 50 cm at the height
of 120 cm from the bud union (Onokpise,
1981). At the time of opening, 25
genotypes showed higher percent of
tappable trees compared to the control
clone RRIC 121. Yet, the control clone
RRISL 205 has reported a higher
percentage of tappable trees than RRIC
121. Genotypes, 98-230, 98-276, 98-41,
98-50, 98-71, 98-19, 98-196, 98-223 and
98-29 have reported 100% tappable trees
at the time of opening for tapping (Table
4). High percentage of tappable trees
ensures a better tapping stand and also
reduces the immature phase.
Dead plants were recorded up to the sixth
yielding year and survival percentage is
given in Table 4. Most probable reasons
for the losses are due to wind damages
and white root disease. A white root
disease patch was identified and the
affected plants were uprooted. The
incidence of wind damage has caused
problems in different forms such as; of
branch snap, trunk snap and uprooting
(Gonçalves et al., 2007). Severely
affected damages were counted as losses.
Percentage of survival varied among
genotypes. Genotypes; 98-124, 98-25,
98-105, 98-201, 98-41, 98-71, 98-51, 98-
54, 98-62, 98-44, 98-64, 98-58, 98-56,
P V A Anushka et al.
135
98-59, 98-74, 98-78, 98-223, 98-29, 98-
278, 98-220, 98-12, 98-224, 98-257, 98-
18, 98-222, 98-149, 98-15 and 98-26
were recorded with 100% survival.
Control clones had better survival
percentages. This attribute helps to
maintain the proper tapping stand
throughout the economic life of the crop
and ultimately a good yield.
Incidences of Tapping Panel Dryness
(TPD) were also recorded (Table 4) as
clonal vulnerability to dryness can be
evaluated only after several years of
tapping (Gonçalves et al., 2007). Only
true cases of dry trees were considered
and those became dry due to wind
damage have been excluded. Incidence
of TPD was observed in almost all the
genotypes and control clones except for
four genotypes; viz. 98-67, 98-29, 98-
220 and 98-193. Genotype 98-84 was the
most susceptible genotype which has
recorded 80% of incidence of dryness,
followed by 98-236, 98-124 and 98-135
with 73% incidence of dryness.
Performance of chemical composition
in latex
In order for a comprehensive analysis,
chemical properties in latex were also
used to identify potential candidate
genotypes aiming to reduce the time
period taken for the clone development
program. Thus, selected eight genotypes
and the control clone RRIC 121 were
subjected to measurements of chemical
composition of selected compounds in
latex (Table 5).
Inorganic phosphorus content of latex is
directly correlated with the metabolic
activity during latex production (Jacob et
al., 1989). This attribute ranged from
6.18 mM in genotype 98-124 to 10.93
mM in genotype 98-80 among the
selected genotypes during high yielding
period. When compared to control clone
RRIC 121, genotypes 98-80 and 98-219
showed significantly higher yields
(Table 1) and also showed significantly
higher inorganic phosphorus during both
high yielding and wintering periods.
Further, genotypes 98-276 and 98-236
showed significantly higher inorganic
phosphorus content than the control
(Table 5).
Sucrose content ranged from 4.68 mM in
genotype 98-219 to 12.19 mM in
genotype 98-236 (Table 5). Sucrose
content in latex may signify a good
loading to the laticifers (Jacob et al.,
1989) which may optimistically affect
latex regeneration. On the other hand,
genotypes 98-80 and 98-219 have
reported higher yields reflecting the high
rate of latex regeneration, thereby
indicating high amount of sucrose
utilization for rubber biosynthesis,
resulting lower sucrose level in latex.
However, comparatively high level of
sucrose content has observed during high
yielding period and a low sucrose level
in wintering season. This revealed the
poor performance in yielding during the
wintering season in genotype 98-80
though it has performed well under
favorable conditions. High level of
sucrose content in genotype 98-236
together with low inorganic phosphorous
content reflects its suitability for
ethephon stimulation based harvesting
systems in future.
Selection based on girth and yield performance of Hevea
136
Table 4. Percentage of tappable trees, percentage survival trees and tapping panel dryness (TPD) of Hevea genotypes from the 1998
HP progarmme compared to the control clones in the small scale trials (1, 2 and 3) at Kuruwita sub-station
Trial 1 Trial 2 Trial 3
Clo
ne
% t
ap
pa
ble
trees
% S
urv
iva
l
% T
PD
Clo
ne
% t
ap
pa
ble
trees
% S
urv
iva
l
%T
PD
Clo
ne
% t
ap
pa
ble
trees
% S
urv
iva
l
% T
PD
98-230 100 87.5 57.14 98-41 100 100 31.25 98-19 100 92.86 53.85
98-276 100 75 33.33 98-50 100 87.5 28.57 98-196 100 92.31 9.09
98-11 93.75 93.75 53.33 98-71 100 100 46.67 98-223 100 100 16.67
98-84 93.75 93.75 80 RL205* 100 93.75 13.33 98-29 100 100 0
98-89 93.75 75 58.33 98-51 93.75 100 50 RL205* 100 84.62 18.18
RC121* 93.75 100 25 98-54 93.75 100 18.75 98-30 92.86 92.86 38.46
RL205* 93.75 100 12.5 98-62 93.75 100 50 98-154 91.67 92.31 30
98-98 93.33 81.25 46.15 98-68 92.86 93.75 66.67 98-278 91.67 100 60
98-219 92.86 87.5 35.71 98-44 87.5 100 20 RC121* 91.67 78.57 30
98-143 87.5 93.75 53.33 98-58 87.5 100 68.75 98-220 86.67 100 0
98-236 87.5 93.75 73.33 98-64 87.5 100 37.5 98-23 84.61 92.31 18.18
98-164 86.67 93.75 33.33 98-73 86.67 93.75 20 98-12 76.9 100 30.77
98-124 81.25 100 73.33 98-77 84.61 81.25 38.46 98-193 70 92.31 0
P V A Anushka et al.
137
Trial 1 Trial 2 Trial 3
Clo
ne
% t
ap
pa
ble
trees
% S
urv
iva
l
% T
PD
Clo
ne
% t
ap
pa
ble
trees
% S
urv
iva
l
%T
PD
Clo
ne
% t
ap
pa
ble
trees
% S
urv
iva
l
% T
PD
98-207 81.25 81.25 30.77 98-07 80 93.75 33.33 RC130* 69.23 92.86 50
98-25 81.25 100 33.33 RC121* 80 93.75 7.14 98-224 69.2 100 28.57
98-83 78.57 81.25 53.85 98-67 75 75 0 98-200 66.67 76.92 22.22
98-105 75 100 56.25 98-56 60 100 40 98-257 66.67 100 58.33
98-135 75 93.75 73.33 98-59 56.25 100 31.25 98-18 64.29 100 14.29
RC130* 75 87.5 71.43 RC130* 53.33 100 57.14 98-38 64.29 92.86 38.46
98-153 68.75 93.75 33.33 98-70 50 93.75 46.67 98-222 54.54 100 33.33
98-237 56.25 93.75 46.67 98-74 43.75 100 37.5 98-149 44.44 100 22.22
98-201 53.33 100 46.67 98-37 26.67 93.75 33.33 98-15 41.67 100 41.67
98-120 50 75 20 98-55 26.67 93.75 14.29 98-194 33.33 93.33 21.43
98-81 46.15 75 50 98-78 12.5 100 37.5 98-26 28.57 100 28.57
98-205 37.5 87.5 28.57 98-80 6.25 93.75 40
Mean 79.04 89.75 15.02 Mean 71.13 95.5 34.72 Mean 74.54 94.755 27.68
SE 3.55 1.76 3.67 SE 5.8 1.28 3.44 SE 4.53 1.38 3.53
Selection based on girth and yield performance of Hevea
138
Table 5. Chemical composition of selected compounds in latex of selected genotypes and the control clone RRIC 121 during high
yielding and wintering season
Means followed by the same letter within a column are not significantly different from one another at p < 0.05
HP
progeny
Sucrose (mM) Inorganic phosphorus
(mM)
Thiol (mM) Polyphenol (mM) Dry rubber content
(%)
High
yielding
Wintering High
yielding
Wintering High
yielding
Wintering High
yielding
Wintering High
yielding
Wintering
98-219 4.68d 1.9g 10.9a 0.87a 0.11cd 0.24a 1.35d 2.08a 49.04e 39.28c
98-80 7.53b 2.61f 10.93a 0.92a 0.18bc 0.02g 1.4cd 1.29f 48.69f 40.72b
98-105 3.74e 5.35b 8.29d 0.48bc 0.13bcd 0.02h 1.13e 1.56d 49.92d 38.68c 98-124 5.19d 2.86ef 6.18e 0.53b 0.11cd 0.10b 1.4cd 1.39e 50.83b 44.64a
98-143 6.14c 3.49d 10.63a 0.39d 0.43a 0.02i 1.09e 1.49d 54.78a 34.77d
98-236 12.2a 4.98bc 9.2c 0.41cd 0.14bcd 0.03f 1.71b 1.66c 50.34c 38.21c
98-276 6.5c 4.59c 9.65b 0.52b 0.08d 0.03c 1.03e 1.50d 40.49i 31.99e
98-68 6.64c 3.2ed 6.28e 0.26e 0.17bc 0.03d 2.65a 2.07a 47.97g 33.71d RRIC 121 6.75c 15.9a 8.43d 0.15f 0.21b 0.03e 1.48c 1.83b 47.44h 44.17a Mean 6.6 4.99 8.94 0.51 0.16 0.06 1.48 1.65 48.83 38.46
CV 6.39 5.06 2.12 7.80 24.45 - 3.57 2.92 - 1.63
Root MSE 0.42 0.25 0.19 0.04 0.04 - 0.05 0.05 - 0.63
P V A Anushka et al.
139
Dry rubber content (DRC) during the
high yielding period ranged from 47.4%
(RRIC 121) to 54.8% (98-143). All the
selected genotypes showed significantly
higher DRC values compared to control
clone RRIC 121. Furthermore,
genotypes 98-124 and 98-236 also
showed high DRC values, 50.8% and
50.3%, respectively. Though genotypes
98-80 and 98-219 showed comparatively
higher DRC, a reduction in DRC was
observed in genotype 98-219 during the
wintering season and therefore 98-80
would be a better genotype than 98-219
(Table 5).
Thiol content in selected genotypes
ranged from 0.08 mM in genotype 98-
276 to 0.43 mM in genotype 98-143
(Table 5). Thiol content in latex has a
direct correlation with latex production
via acting as a potential activator for key
enzymes such as pyruvate kinase and
invertase (Jacob et al., 1989). In
addition, they act as antioxidants that
protect cells against damages caused by
reactive oxygen species (De Costa et al.,
2006). Genotypes 98-219 and 98-124
showed comparatively higher thiol
content even during the wintering
season.
High level of phenols could be resulted
due to reduced levels of polyphenol
oxidase enzyme, which is a key enzyme
in latex coagulation (Coupe and
Chrestin, 1989). In addition, high level of
polyphenol content in latex may cause
discoloration in the presence of
polyphenol oxidase enzyme (Yapa,
1976). Polyphenol content in selected
genotypes ranged from 1.03 mM in
genotype 98-276 to 2.65 mM in genotype
98-68. Genotype 98-68 may produce
rubber with high color index due to
higher level of polyphenol content.
Genotypes 98-219, 98-80, 98-105, 98-
124, 98-143 and 98-276 showed
significantly lower level of polyphenol
content compared to the control RRIC
121 during the high yielding period
(Table 5).
Conclusion
A proportion of 63% of new genotypes
showed higher mean yield compared to
the control clones. Genotypes 98-80 and
98-219 were the top-ranking genotypes
that recorded the highest mean yields.
When compared to the control clones,
82% of genotypes have represented
higher or comparable mean girth. In
terms of girth, 18% of genotypes showed
more than 70 cm of mean girth and those
could be considered as potential
genotypes to develop vigorous timber
clones in the future. Further, these
genotypes showed better yields
compared to control clones. Genotypes
98-276, 98-68 and 98-223 recorded
respective girth values of 80.6 cm, 76.5
cm and 71 cm which were the top most
at the final year, based on their girth.
With respect to increment in girth, 12%
of the genotypes showed an increment of
nearly 7 cm/year before opening for
tapping. Genotypes 98-223, 98-50 and
98-276 have recorded the highest girth
increments, viz. 2.2 cm, 2.0 cm and 1.9
cm, respectively after commencement of
tapping. In 25 genotypes, higher percent
of tappable trees than control, RRIC 121
was observed. According to the chemical
properties in latex; genotypes, 98-80 and
98-219 performed well based on DRC,
sucrose and inorganic phosphorus. To
Selection based on girth and yield performance of Hevea
140
confirm these results, further evaluation
of chemical composition in latex should
be carried out in a field tapped in virgin
panel during the next evaluation stage.
Acknowledgements
Authors would like to acknowledge the
technical support given by the staff of the
Genetics and Plant Breeding Department
at the Kuruwita sub-station and the staff
of the Biochemistry and Physiology
Department of the Rubber Research
Institute of Sri Lanka.
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Address for correspondence: Mrs P V A
Anushka, Former Research Officer and Dr
(Mrs) S P Withanage, Head, Genetics &
Plant Breeding Dept., Rubber Research
Institute of Sri Lanka, Nivithigalakele,
Matugama, Sri Lanka.
e-mail: [email protected];